微束分析技术在研究伴生金元素赋存状态中的应用

The Application of the Microbeam Analysis Technique in Associated Gold and Its Occurrence State

运用微束分析技术扫描电子显微镜(SEM)及其配套的背散射电子像功能,特征X射线线扫描、面扫描功能,能谱仪(EDAX)鉴定功能,观察里伍铜矿矿石中纳米级至微米级的伴生金(超微细金)矿物,获取其形貌照片、能谱图和定性定量分析结果,得到了清晰的金元素及与其共生的元素线、面分布图像,查明了里伍铜矿中的金元素是以类质同象的形式分布于含银的铋矿物和金银矿中,含银的铋矿物和金银矿分布在黄铜矿与磁黄铁矿的裂隙中及含锰的铁闪锌矿中,排除了基体成分的干扰,载金矿物颗粒至少大于20 nm。该方法操作简便,过程简单,分析结果直观、可靠,提高了研究伴生金元素赋存状态的效率。测试的样品为里伍铜矿热液型矿石,经分析形成于燕山中晚期(104～142.2 Ma),为局部构造运动和岩浆期后热液使成矿元素再富集成矿的地质产物,晚于主成矿期——燕山中期。里伍铜矿中Ag和Au的质量比值为1.38～4.59,推测伴生金的成矿温度应小于或等于227℃。里伍铜矿在成矿过程中至少经历了早期的中高温热液阶段和晚期的中低温热液阶段,早期大量硫化物的析出和晚期中低温绿泥石、绢云母矿物的大量出现也证实了这一过程的存在。

In this paper,the technique of advanced microbeam analysis using a Scanning Electronic Microscope（with back scattered electron photo）,characteristic X-ray line scanning,line-by-line scanning and Energy Dispersive Analysis identification were used to observe micro-fine gold hosted in Liwu copper ores.The micro photos,energy dispersive spectrum,chemical compositions of nanometer-grade and micrometer-grade gold provided a clear line and plane distribution pictures of gold and other coexisting elements.Gold in Liwu copper ores was hosted as isomorphism in Ag-bearing kustelite and bismuth minerals,which disseminate in the cracks of chalcopyrite,pyrrhotite and Mn bearing marmatite.The grain size of the gold carrier minerals is more than 20 nm after matrix interferences correction.This method is easy and simple to obtain reliable and visual analytical results,which significantly increase the efficiency of studying the occurrence states of gold.The hydrothermal ore samples from the Liwu Cu deposit were formed at the middle-late stage of Yanshan 104-142.2 Ma by tectonic movement and metallogenic hydrothermal activities,which was later than the peak mineralization at the middle stage of Yanshan.The ratios of Ag/Au are from 1.38 to 4.59,which indicate the metallogenic temperature was no more than 227℃.The Sulfide ore precipitation and occurrence of chlorite and sericite indicate the Liwu Cu deposit has two mineralization stages as early high-middle temperature hydrothermal activities and late middle-low temperature hydrothermal activities.